Add more client libraries

[holly-hacker]

This repo only lists a few client-side HTTP libraries, while there are many that could be useful in various circumstances:

• attohttpc (lightweight, no async)
• curl (bindings to libcurl)
• isahc (higher level http client built on curl)
• minreq (very lightweight, no async)
• surf (multiple http backends, such as hyper, curl, window.fetch on wasm)
• ureq (lightweight, no async)

[flosse]

@holly-hacker Would you mind to create a PR?